In known devices of the aforesaid type the elastic element consists simply of a spring. The main drawback of known devices is their noise. In this respect the rolling movement of the watercraft results in continuous stressing of the device, with consequent stressing of the spring which in extending or compressing to return to its rest position produces a very annoying noise. It is well known that an extending spring is easily subject to yielding and, in the limit, to breakage due to excess load. In the aforesaid known devices with an extending spring, this drawback is obviated or at least limited by the addition of a by-pass safety chain which however, when in operation, eliminates the damping effect with the inevitable consequence that impact forces arise.
It should also be noted that as said devices are constructed completely of rigid materials, they can cause damage to the bottom of the watercraft by bruising and/or rubbing during mooring and during pulling-in of the mooring line or chain. In addition, known devices have an "open" structure and are therefore completely exposed to the water which, particularly if sea-water, deteriorates the device components and especially the elastic element. In this respect with the passage of time this latter, because of the action of the water, tends to rust and/or become less elastic. This on the one hand causes a further increase in the noise of the device and on the other hand results in lower device efficiency.